A unitary humidity exchange cell (or HUX), as the name implies, is an element of a device that is capable of transferring water or other highly polar liquid or gas from one side of the cell to the other by action of a difference in some quantity or gradient across said cell. A key operational characteristic of the HUX cell is that a difference of some intensive or extensive property of the system (relative to the surrounding) leads to a gradient change of said property to effect mass transfer of water or some other highly polar liquid or gas from one side of the membrane to the other with or without an accompanying flow of electrons, protons, ions or molecules other than said water or other highly polar liquid or gas. It is under the influence of this property that exchange in liquid water or some other highly polar liquid or gas occurs across the permaselective membrane. This transfer of water or some other highly polar liquid or gas may or may not be accompanied by evaporation of said water or other highly polar liquid or gas into (or from) the stream by the absorption of heat or adiabatically or by some other thermodynamic means; for example the condensation or evaporation of liquid water or some other highly polar liquid or gas or the simple diffusion of water or some other highly polar liquid or gas into a pure liquid stream. A finite gradient across the membrane must exist in some quantity; examples are vapor pressure, osmotic or hydrostatic pressure, chemical, thermochemical, electrochemical, magnetochemical potential, as well as thermal (temperature or heat content), electric, electromagnetic, thermoelectric, or electrothermal potential difference. There must be at least two streams, one supplied to each surface of said membrane by some means either as a liquid or vapor flow each of which differs in at least one identical property of the system. The system attempts to reach a thermodynamic equilibrium by transporting water or some other highly polar liquid or gas from one stream to the other. The orientation of the streams to one another is considered arbitrary for the invention; these may be counter flow, coflow, crossflow, mixed flow or any other geometric arrangement of one or more streams. Water or some other highly polar liquid or gas transport (e.g. hydrodynamic, electrohydrodynamic, magnetohydrodynamic, diffusion, migration, or convection) occurs until the imposed gradient can no longer meet the physicochemical constraints of the system required to sustain the motion. In many cases, the exchange of water or some other highly polar liquid or gas between the streams is slow, but this may be due to some other limiting factor, such as, boundary layer effects, concentration polarization, hydrostatic pressure lag or gravity, surface tension effects, and convective or frictional effects. However, once these engineering design or system effects are minimized, inevitably, the exchange or transport of water or some other highly polar liquid or gas is rate-limiting if the permeability of the membrane to water or some other highly polar liquid or gas is poor. Hence, an important object of the invention is that hydrophilic polymer membrane has high permeability to water or some other highly polar liquid or gas; more than necessary for most applications. The hydrophilic polymer membrane (or formulation) must be mechanically supported and there must be means to supply the two streams to said surfaces. A second object of the invention is that the three sub-elements be fabricated as one unit by conventional means at low cost. This requires that the hydrophilic polymer wet the support, achieve intimate contact and demonstrate exceptional adhesion to it. Therefore, a third object of the invention is that the support be a polyolefin or blend thereof such that one component of said hydrophilic polymer is similar in chemical structure to one component of the support.
HUX cell design is general in that water (liquid or vapor) or other highly polar material (liquid or vapor) can be transferred between any two fluids. Examples of applications are per-vaporation, humidification and dehumidification of fuel cell streams in stacks and devices, drying gases at pressure, tertiary oil recovery, process control for chemical manufacture of chemicals for which water is a reactant, isolation of minerals from mining fluids, industrial separation of oil-water emulsions, microfiltration and ultrafiltration of colloidal suspensions and biological or organic macromolecules for purification, maintaining water content of methanol in direct methanol fuel cells, reverse osmosis for isolation of fresh water from brine, electrolysis cells, dialysis, electro-dialysis, piezo-dialysis, electro-osmosis and chloro-alkali cells.